Thermal Stability of Self-Assembled Monolayers from Alkylchlorosilanes

Abstract

Contact angle measurements and scanning force microscopy (SFM) have been used to study the morphology of self-assembled monolayers of octadecyltrichlorosilane (OTS) and undecyltrichlorosilane (UTS) on silicon oxide surfaces as a function of annealing temperature. Characterization of the monolayers before annealing indicates that the as-formed monolayers cover the substrate fully and have thicknesses of 2.9 and 1.5 nm, respectively, with the average surface having a roughness of approximately 0.3 nm. Water contact angle results and SFM roughness analysis showed that UTS monolayers annealed for 2 h at temperatures over 125 °C exhibited permanent changes in monolayer structure. Experimental data indicated a higher transition temperature for permanent structural changes for the OTS monolayers. Water contact angle measurements indicated a transition centered at 125 °C, hexadecane contact angle measurements indicated a transition around 130 °C, and SFM indicated a transition centered at 155 °C for OTS monolayers. We have observed that contact angle measurements can be sensitive to surface structure on an angstrom length scale. These results observed after 2 h are not equilibrium results, as evidenced by the further development in the monolayer after an anneal for 5 h. Thermodynamic considerations support the earlier (lower temperature) changes observed for UTS than for OTS monolayers. The observed transition is likely the result of hydrolysis of the organic molecules by water molecules existing at the monolayer-substrate interface.

Gestaltung der Siliciumoxidoberfläche durch selbstorganisierte Monoschichten

“…Grund für diese Stabilität sind die partielle Vernetzung der Moleküle und die mögliche kovalente Verankerung am Substrat. An der Luft sind SAMs von OTS bis zu einer Temperatur von 150 8C stabil, [17,[77][78][79][80] und erst bei Temperaturen darüber verändert sich die Struktur der Monoschicht irreversibel. Perfluorierte SAMs scheinen sogar noch beständiger gegen thermische Zersetzung zu sein: [78,81] Srinivasan et al berichteten von 1H,1H,2H,2H-Perfluordecyltrichlorsilan-Beschichtungen, die sogar bis 400 8C intakt bleiben.…”

Ultrathin liquid films under alternating intermolecular potential fields and capillary force

“…17 On the other hand, the film fills the cavity of the mold to a thickness of about 5.4 nm for a relatively small channel width ͑150 nm͒ as shown in Fig. 3͑b͒, which results from capillary rise.…”

“…Silicon dioxide wafer that was used as a substrate was cleaned by ultrasonic treatment in trichloroethylene and methanol for 5 min each and dried in nitrogen. The substrate was then dipped in an octadecanethiol ͑ODT, CH 3 -(CH 2 ) 17 -SH͒/ethanol solution ͑0.1 g/50 ml͒ for 5 min to 1 h.…”

Nanostructure of supported lipid bilayers in water

“…The grafting of the lipo-PEG to the Si surface can be realized by silane chemistry. 33,34 This reaction is, however, very sensitive to tiny amount of water and cross-linking is difficult to avoid. Therefore, we have chosen a multistep reaction.…”